Field of the Invention
This invention relates to a brushless DC motor, and particularly to reducing core loss caused in a return yoke for obtaining a motor of high speed rotation.
There are a variety of systems known for a brushless DC motor. A construction of being manufactured by the assignee of the present application in its own factory is shown in FIG. 5.
Namely, in FIG. 5, numeral 1 is a stator housing of a disk shape, a rotary axis 3 is rotatably mounted in bearing portion 2 mounted in a center portion of said stator housing 1.
A rotor yoke 4 of a disk shape is fixedly mounted to an end portion of said rotary axis 3 as one body, a magnet member 5 of ring shape is fixedly mounted under said rotor yoke 4 as one body.
A return yoke 6 of a ring disk is fixedly mounted on one surfacce of said stator housing 1, said return yoke 6 is composed of an iron plate.
Further, a plurality of a driving coils 7 of a triangle shape are mounted on said return yoke 6 as one body.
Referring now to the operation of the above noted brushless DC motor:
In the condition of FIG. 5, the certain driving signals are applied to said driving coils 7 through an electronic switching means (not shown), said rotor yoke 4 is continuously rotated by a magnetic operation in relation of said magnet member 5, said driving coil 7 and said return yoke 6.
With the above described brushless DC motor, there are presented the following various problems.
Core loss increases in proportion to a self-multiplication of rotary speed of said rotor yoke 4, whereby it is very difficult to obtain a preferable efficiency and power consumption for a high speed rotation about 2000 RPM such as a spindle motor for floppy disk (FDD) and VTR.
Further, according to the increase of said core loss, in case said motor was employed for said FDD and VTR, circuit parts of said FDD and VRT are injured by heat therefrom, whereby a characteristic of said FDD and VTR becomes worse and life thereof becomes lower.